Farming Mimiron's Head / Invincible - lockout "trick"?

Is it possible to save my alt to Ulduar with only Yogg-Saron alive, then having my friend enter the lockout, leaving the instance on my alt and joining the run on my main? Could I save this reset if I extend it on my alt every week, then kill Yogg-Saron on my main? The main issue I have with farming this mount is having to clear the whole instance every week, it would be much easier if I could just grab my alt's reset every week.

The same goes for ICC25, could I just have my alt give me a 11/12 hc reset every week?

Is it possible to save my alt to Ulduar with only Yogg-Saron alive, then having my friend enter the lockout, leaving the instance on my alt and joining the run on my main?

A: Yes, you could use your alt to clear Ulduar and then enter with your main so long as the alt has party lead.

Could I save this reset if I extend it on my alt every week, then kill Yogg-Saron on my main?

A: By this do you mean... Clear it once on the alt and just keep re-extending the lockout each week
while killing Yogg on your main? No. Why? All raids come with a unique ID. Once Yogg is dead, when the alt re-extends
the lockout you'd essentially be extending it with the Yogg kill included.

You can swap the lockouts from your alt to your main by having a friend zone in to 'hold' the lockout while you swap toons, but there is no 'trick' as you describe. If you kill Yogg on that lockout, it'll save your alt to Yogg as well.

Raid ID's still work the same as they always did minus the auto-save upon entering the instance.
The ID belongs to the alt, so yes could consider that personal but the main toon is entering said
instance on the ID belonging to the alt therefore eliminating whatever open raid ID the main toon had.

There's just no trick to getting around clearing the bosses leading up to Yogg/LK.

Lockouts are personal for WotLK raids and up, so if you clear up to Yogg-Saron on an alt, than invite a friend to zone in and hold the lockout for you while you switch to your main, you'll be able to kill Yogg on your main without your alt getting saved to him.

The next week, you extend the lockout on your alt, and redo the steps above. You can do this for as long as you want.

Lockouts are personal for WotLK raids and up, so if you clear up to Yogg-Saron on an alt, than invite a friend to zone in and hold the lockout for you while you switch to your main, you'll be able to kill Yogg on your main without your alt getting saved to him.

The next week, you extend the lockout on your alt, and redo the steps above. You can do this for as long as you want.

Yes, this was my intention, but other posters have said this won't work. Did you personally do this?

I've got 2 accounts, on account A I have a char with a 1/2 Throne Of Four Winds save that I extend every week, I'm able to make several raids for main and alts to solo Al'akir weekly. I imagine it is possible to do the same with ICC and Ulduar, plus you could clear 11/12 normal 10 man ICC and switch to 25 man hc as they changed it.

I farm al'akir everyweek and just have a friend who keeps the save for me so I can skip the first boss. He just invites me to a group and I enter the instance. Having the instance mode set to normal wont get you saved when you enter but if you set the instance to heroic you will get asked to be saved when you enter so I'm almost certian you could do this with alts instead of a friend for ICC. Uldaur might be differnet becuase it does not have a heroic mode.

I've done this since... FL or so I think.
Have an alt saved with cleared up to Yogg, start a group with that alt and extend lockout, join with the chars me and my friends want to use, enter the instance (my friends would enter while I hold the raid on the alt), once they're in, leave the group with the alt and relog my main, enter the instance and kill the boss. Next week just re-extend my alt's lockout again and repeat.

For normals and such the lockouts are personal (there was no HC setting pre-ToC, so the lockouts are personal).
As for ICC we clear 11/12 10 normal (with an alt in on the 11th kill to get it saved to 11/12), then leave group and set to 25 HC on our mains and kill.
Next week we extend lockout of the alt, enter on mains and leave the group with the alt, set it to 25 HC and kill LK again. Simples.
Takes about 10 min to do both bosses per week. We do the same for Ultraxion.

I farm icc/ulduar like that for ... probably a year, incomming kill#100 on yogg (over all my alts that I farm it on aswell) and I've yet to see a mount drop , around 9 kills on lk tho, haven't rly tried him untill 5.1 (4-manning him now w/o to much trouble)

Is it possible to save my alt to Ulduar with only Yogg-Saron alive, then having my friend enter the lockout, leaving the instance on my alt and joining the run on my main? Could I save this reset if I extend it on my alt every week, then kill Yogg-Saron on my main? The main issue I have with farming this mount is having to clear the whole instance every week, it would be much easier if I could just grab my alt's reset every week.

The same goes for ICC25, could I just have my alt give me a 11/12 hc reset every week?

You're almost right with the Ulduar lockout but there's one important thing you forgot: After doing the character swapping to get to Yogg on your main you must remove your alt from the raid else they'll get locked to the kill even if they weren't there for the kill.
As for ICC your alt must only have a normal lockout to LK. Once you get your main in and remove your alt from group then you can convert to heroic (yes you can kill heroic LK on a full normal lockout, it's been this way since the cata pre-patch).

Is it possible to save my alt to Ulduar with only Yogg-Saron alive, then having my friend enter the lockout, leaving the instance on my alt and joining the run on my main? Could I save this reset if I extend it on my alt every week, then kill Yogg-Saron on my main? The main issue I have with farming this mount is having to clear the whole instance every week, it would be much easier if I could just grab my alt's reset every week.

The same goes for ICC25, could I just have my alt give me a 11/12 hc reset every week?

Yes, this is what I do, my alt has a save to LK, Al'akir, and Yogg. All I do is log the alt on every week, log on a friend's account and invite it to a group, log off and log on my main, join the group and beat things up. I don't know what people are talking about "removing the alt from the raid or it'll get saved", I've never had that happen to me.